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Full text of "Operant Measurement of Subjective Visual Acuity in Non-Verbal Children"

;> ABSTRACT *"*•** ^a^-j j 

The present experimentation undertook the problem of developing a reliable 
measuring procedure for "subjective distance visual acuity" in order to make possible 
the examination of non-verbal retarded children. Five non-verbal retarded children 
and two literate "normal" adults were examined. The two adults were included in the 
experiment so that verbal communication xd-th them could validate certain assumptions 
regarding the experimental procedures. 

By utilizing a lever press as the criterion response signifying a visual discrim- 
ination and employing the Snellen "E" discriminandaj a reliable subjective measure 
was obtained, not unlike those measures taken from verbal adults. Contrary to ante- 
cedent procedures, a relatively precise measurem.ent of subjective acuity was shown 
to be obtainable from non-verbal retarded children. Additionally j the present pro- 
cedure was successful in evaluating the effectiveness of prosthetic lenses previously 

prescribed for two of the children. 

Paaphlot Fllfi 

Proto39lonal Library 

IMKC/APB 



A^^wi**'' •••■ 









Operant measurement 

of subjective visual acuity 

in non-verbal children 

2 
Joel Kacht 

There exists a population of children x<iho do not manifest appropriate behaviors 
required for an accurate subjective visual acuity examination. IJhether they are 
very young or mentally retarded, these children lack a response repertoire which 
allows them to come under the necessary stimulus control needed for an acuity measure- 
ment. They may not speak or read. Frequently, such children are active and not 
confined easily to an examination chair for any length of time. They fail to follow 
verbal commands given by the examiner and do not focus on a stimulus object when it 
becomes necessary. They are often described as either "insufficiently intelligent," 
"insufficiently mature," or "unmotivated' to the degree required for ocular examin- 
ations. 

Parents of such children are frequently informed to bring the child back in six 
months when he becomes more mature" and, on occasion, are given letter cards and 
instructed to train the child in recognition of the letters so that on returning to 
the physician the child can be tested. Present indications are that with severely 
retarded children, the mere passing of time is small help. Untrained mothers are 
generally incapable of coping with the difficult discrimination training required in 
teaching a child to recognize visual sjmibols. The result is that many children are 
never given adequate visual examinations, and impairments may be undetected and, 
hence, uncorrected. 
Visual Acuity 

The ability of the visual mechanisms to distinguish small spatial separations 

or intervals between portions of the visual field is known as visual aciity (English 

& English, 1958). It is determined by the smallest form that stimulates a retinal 

^This research was in partial fulfillment of the Ph.D. degree under the chair- 
manship of Dr. R. Keith Van Wagenen. The author is indebted for his chairman's 
advice and assistance. 

2 

Now at the University of South Florida, Department of Educational Psychology. 



Uo 



image, and is measured by the smallest object waich can be clearly seen at a certain 
distance (Duke-Elder, 1965). In humans^ distance acuity is measured with a letter 
chart (Havener s 1963), e.g., Snellen chart, which is placed 20 feet from the reader. 
Recording of acuity is by a ratio. The numerator represents the distance from the 
chart to the reader and the denominator indicates the distance at which the normal 
eye reads the line (Duke-Elder, 1965). 

Two different measures of acuity. An "'objective" measure of acuity is obtained 
when an examiner employs a retinoscope and an ophthalmoscope to observe the internal 
parts of the eye. A "subjective'' measure of acuity is obtained by placing a chart 
in front of a subject and requiring him. to report what he sees. There are various 
letters of different size printed on the eye charts. The subjective examination 
generally is em.ployed for purposes of refining the objective measurements as well 
as estimating distance visual acuity. 

Relatively minimal behavior is required of a subject to complete an objective 
measurement of visual acuity. Having a patient sit in a chair with eyes remaining 
motionless generally is sufficient. On the other hand, to obtain a subjective 
measure of acuity j a subject must have a complex behavior repretoire before necessary 
information can be conveyed to the examiner. He must listen to verbal commands, 
interpret stimulus objects, and manifest appropriate responses. 

Studies investigating sensory thresholds in infrahuman organisms are abundant 
(Blough, 1957: Blough, 1958 | Blough & Schrier, 1963; Adler & Dalland, 1959; Elliot 
et al., 1962^ Heise, 1953; Yarczower et al., 1966). Procedures developed by these 
researchers have afforded precise measurement of various acuity thresholds in infra- 
human subjects. However, review of the research failed to evidence comparable 
methods for obtaining reliable estimates of subjective visual acuity in non-verbal 
children. Explanations offered accounting for the difficulty of securing precise 
estimates of acuity v/ith young or retarded children are varied. 

Duke-Elder (1965) stated that ordinary tests of subjective acuity are totally 
dependent upon the patient's cooperation and may be inadequate for young children. 



_0. 



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™Jaiingerers and. illiterates- Allen (1S57) added that there are always some children 
up to five years of age who are "unable or unwilling" to cooperate for acuity measure- 
ments . 

Adler (1962) indicated that since subjective methods of refraction depend upon 
the patient distinguishing between letters on the Snellen chart, the procedure is 
applicable only to patients old enough to respond appropriately to an examiner's 
verbal statements. Hence s Adler concluded that the subjective measurement of visual 
acuity was of little value in children less than seven to eight years of age, or for 
"ignorant'" adults. 

Adler (1950) held the opinion that when an individual was required to respond 
to a Snellen chart, various complex behaviors V7ere necessary: "the power of attention, 
willingness and ability to read, motivation and cooperation." He further stated that 
there can be little doubt that failure to measure accurately most children is due to 
"their lack of cooperation and their low level of intellectual functioning,'" 

Meyerson and Michael (1960), in reviewing research on auditory thresholds, 
encountered measurement reliability problems similar to those involved in measuring 
vision. They reported that almost all studies of auditory acuity of mentally retarded 
children demonstrate them to have considerably higher incidence of hearing loss than 
are found in the normal population. They concluded that these findings may not be 
justified, for their experimental data did not support the purportedly higher inci- 
dence of physiological impairment. 

One explanation accounting for the higher incidence of impairment may be a 
function of the procedures employed for the estimation of the sensory threshold. In 
view of the difficulties expressed by many examiners when attempting acuity measure- 
ments in "uncooperative" or "unmotivated" children, Meyerson and Michael (1960) 
asserted that a method is required whereby the examiner can be reasonably assured 
that his findings refer to limits in the child's ability to make appropriate discrim- 
inations and not to behavior deficits. They reasoned that any procedure so devised 
must not confound failure in revealing a discrimination with failure in sensation. 

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Several prodedures are available for oltainirig visual acuity estliTiatos fron 
children. Reviews of these methods are provided by Blackhurst and Radke (1968) and 
Wolfe and MacPherson (1960) . The procedures include grading of the opticokinetic 
nystagmus (Gorman et al., 1957), Ivory Ball test (Duke-Elder, 1965)5 Finger test 
(Sjogren, 1939), Picture test (Gundersen^ 1955), Illiterate E test (Duke-Elder, 1965) 
Allen Picture test (Allen, 1957), Massachusetts Vision test (Leverett, 1957), Key- 
stone Telebinocular test (Kelly, 1957). 

Problems are found with many of the above procedures. There is often a lack of 
precision in the stimulus objects employed. The criterion responses employed to 
measure acuity are at times ambiguous and difficult to observe. No mention is made 
regarding how to bring a subject's behavior under stimulus control. There is no 
assurance that a child is responding to the stimulus objects presented rather than 
"cues" being provided by the examiner. 
Current Investigation 

The present study undertook the development of a procedure for measuring the 
subjective distance acuity of very young or retarded children. For practical utility 
a method must incorporate specific requisites into its procedure. First, the 
operations must lead to accurate measurement of the criterion response. Hhen the 
child responds to the stimuli presented him, his response must be unambiguous, 
observable, and consistent. Second, the stimulus object presented must have a pre- 
cise measurable quality in order to facilitate interpretation and communication. 
Third, there must be a means of maintaining responding until an examination can be 
completed. If the subject fails to respond to the stimuli, there must be an accurate 
explanation why the response was not emitted. Finally, an assurance is required that 
the subject is responding to the stimulus object presented and not to some extraneous 
cue. 
Procedure 

The experimental sample consisted of five children and two adults. The adults 
served the function of validating the initial procedures employed with the 
For a detailed account of the procedure see Macht (1969) . 

„4- 



experimental children. The general procedure was to condition an operant response 
to a bar press apparatus. When this was accomplished, the subject vjas taught to make 
the lever press in the presence of one visual stimulus, i^hiie avoiding the response 
in the presence of a second one. The visual symbols used vrere letter '"Es" which 
duplicated various Snellen letter sizes (Duke-Elder, 1965). 

The procedure had four arbitrarily defined phases. However, the phases were 
flexible and on occasion overlapped. In the initial phase j the subject v/as taught 
to press the lever. In the second phase, he was conditioned to press the lever in 
response to light but not to press it in the absence of light. In the third phase, 
the experimenter "faded in" the stimulus letters to establish a aiscrininatiou between 
a forward facing and a reversed '"E". Lever pressing was then under control of the 
letter presented. In the final phase, the subject's distance visual acuity was 
measured by decreasing the size of the E-discriminanda and moving the subject away 
from the stimulus letters. 

Experimental analysis of the response behavior of one subject at a time was 
carried out v;ith intersubject replications (Sidman, 1960). Intrasubject threshold 
crossing were utilized for reliability purposes. The dependent measures were the 
number of correct and incorrect responses under the independent variable conditions 
of stimulus card size and distance from the stimulus wheel which housed the stimulus 
cards. The stimulus wheel, response table, and "E" letters are described elsewhere 
(Kacht, 1969). 

The experimenter worked behind a cardboard blind over which he could observe 
the subject by rising slightly from his chair. This arrangement prevented subjects 
from watching the experimenter's facial expressions and hand movements which conceiv- 
ably x^;ere capable of providing cues to the learner. 

Noises from the counters and switch boxes employed to count responses and pulse 
the cumulative recorder, were the same for both stimulus conditions, i.e., SD, " delt?. 

The presentation of the SD, i.e., forward "E" and S-delta, i.e., reversed "E" 
cards were randomized. Approximately equal frequencies of SD, S-delta periods were 



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' '.I -?.■? 

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maintained = Variation of the number of periods was a function of the SD, S-delta 
presentation sequence. 

A trial was defined as either one response to a discriminandum or a specified 
lapse of timeo The SD condition was t'smiinated when one response on the lever had 
been counted or when no response occurred ^dLthin a three-second period of time. 
Termination of the S~delta condition occurred after one response or after ten seconds 
of no responding. If the subject responded several times in an SD period, he was 
credited with only one correct response and reinforced once. The "reinforcer" was 
some consumable stimulus, e.g., M & M, pretzels, cereal. If the subject responded 
several times in an S-delta period, only the initial response was punished and he was 
credited with one error response. "'Punishment" was a slap on the responding hand 
paired with a loud verbal statement "no." 

The stimulus cards employed to train a subject to discriminate the forward and 
reversed '"Es'" vjere one and one-eighth inches larger than the 20/200 "E" cards. They 
were called "'criterion" cards. 

Phase one. The subject was placed in a chair 29 inches from the stimulus wheel. 
The subject v^as in a comfortable position so that he could press the lever pad located 
on the response table, while facing the stimulus vrheel that held the visual discrim- 
inanda, i.e., black letter "E" mounted on white paper backing. Before beginning the 
discrimination trials, the experimenter placed two stimulus cards into bipolar slots 
on the front of the stimulus wheel. One was a large forward facing letter "E," 
This was the discriminative stimulus (SD) criterion card. Reinforcement was contin- 
gent upon the subject pressing the lever in the presence of this card. The SD card 
was placed in the bottom slot of the v/heel, A second "E" card, with the same dimen- 
sions as the first was placed in the top slot of hhe wheel. When the wheel was turned 
the ''E' at the top came to the bottom and appeared as a reversed "E." This reversed 
' E" was called the S-delta criterion card, in the presence of which the child was not 
to respond on the lever. During phase one, the experimenter placed a piece of black 
drawing paper over the S-delta "E" card to prevent subject from viewing the letter. 



■' r J/^^:.^; 'H 



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- ■..■ •<■ 
-' • I 



As the subject scanned the stiraulus iirheelj he saw only the SD "E" card on the bottom, 
and the black paper on the top. The wheel v/as not turned in phase one« 

The experimenter sat beside the subject. He held a switch in his hand which 
controlled bulbs positioned in a box located behind the bottom card. All lights 
in the experimental rooms excluding the bulbs behind the stimulus card, were turned 
off. The effect of illumination from behind the card was to "project" a clear image 
of the SD "E*' card to the subject. All lever press responses emitted under these 
conditions were reinforced. 

Phase two. The second phase began when the experimenter observed a pause in the 
subject's stable lever pressing behavior. When the pause occurred, lights behind the 
SD 'E" card were turned off. Lights off during this phase was called the S-delta 
period. If the subject pressed the lever in the S-delta condition, the experimenter 
said loudly, '"no" and paired the verbalization with a slight slap on the subject's 
responding hand. After a few seconds of total darkness and no lever responding, the 
bulbs were illuminated and lever pressing behavior was reinforced. The initial 
S-delta periods xjere brief, i.e., 2-3 seconds. The latter S-delta periods were 
gradually increased to a maximum of ten seconds. This procedure continued until the 
subject emitted a consistent rate of responding in SB, ioe., bulbs on, while not 
responding in the dark S-delta period. 

When appropriate SD, S-delta behavior was emitted, the subject's behavior x^as 
brought under control of the black card rather than turning off the bulbs. This was 
accomplished by rotating the stimulus wheel so that the black card cover v:' th.s buti^^ 
preventing light from coming through. The S-delta condition was now defined as the 
black card covering the bulbs. Criterion behavior in phase two was defined as press- 
ing the lever in the presence of the forxjard "E" with the lights on, Xiihile not emitt- 
ing lever pressing in zhe. presence of the black card. 

P hase three. Behind the black card x-7as a reversed letter "E" x\rith exact dimen- 
sions of the SD "E." The purpose of phase three was to successively remove the black 
card bringing the subject's S-delta lever behavior under control of the reversed "E." 

-7" 



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The experimenter proceeded as follo;;ss he turned the wheel positioning the SD 
"E" on the bottom and reinforced lever pressing. He next inverted the wheel bringing 
the S-delta black card to the bottom and waited briefly. Again the SD procedure 
was executed. After several reinforced lever presses j the experimenter rotated the 
wheel bringing the black card to the bottom. The experimenter removed the black 
card and replaced it with a smaller black card which covered less of the reversed "E.'" 
This black card had 0,25 inch of black paper removed from the top and bottam, the 
width remaining the same. Eleven black cards were used successively each of which 
was progressively 0.5 inch smaller than the former in its vertical dimension. The 
dimensions of the eleventh card were 8<l5 in, wide, 0.25-in high. The center of the 
black paper corresponded to the center of the white paper backing. If a subject 
failed to respond appropriately to the ^.ntirely exposed S-delta "E" after the 
eleventh fading strip was removed, the strip Xiras replaced at the center of the "E" 
and gradually noved " dovm'' the paper. The eleventh strip V7as gradually faded out by 
placing it lower on each new S-delta trial. TJhen the subject responded to the for- 
ward SD "E," while not responding to the reversed S-delta "E", lever pressing behavior 
was under control of the directionality of the "Es." 

Phase four. The measurement of subjective distance acuity occurred in this 
phase. I'Jhen the subject's lever pressing behavior was under control of the "Es,'* 
he vas moved from the stimulus wheel until bar pressing failed to occur according to 
the required criteria. In addition to the ''E'" criterion cards employed in phases one, 
two J and three, six pairs of cards vrere constructed according to the criteria 
suggested by Duke-Elder (1965) , that were identical topographical representations to 
Snellen's ^'Es/' i.e., 20/200, 20/100, 20/70, 20/50, 20/30, 20/20. 

A first step in measuring distance acuity i^as to present the criterion cards to 
the subject at a distance of 2^" inches from the stimulus wheel. If appropriate 
responding was observed, the subject v/as moved to a distance of 47 inches from the 
wheel, then to 71 inches, 95 inches, 119 inches, 143 inches, 167 inches, 191 inches, 
215 inches, and finally 240 inches. There was no significance for the chosen 

approximate 24"in, distance increments other than convenience. 

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• Increasing the distance between subject and discriminanda was continued as long 
as appropriate responding was manifest. Final decision regarding appropriate respond- 
ing was based on frequencies of SD, S-delta lever responding in relation to the num- 
ber of SD, S-delta presentations. 

If a subject responded correctly to the criterion cards at 2A0 inches, he was 
returned to the 29-in. distance and a nex^ pair of cards, 20/200, was placed on the 
stimulus V7heel. The subject was again moved from the 20/200 cards by the same incre- 
ments as with the criterion SD, S-delta E'" cards. If the subject successfully 
responded at 2A0 inches to the 20/200 cards, he was again returned to the 2? -ii-t. 
distance mark, and the 20/100 cards introduced. This procedure continued until the 
subject either terminated all lever pressing behavior or until there was a marked 
increase in S-delta responding and a significant reduction of SD responding. 

The reliability of the threshold. Ilhen a subject ceased responding appropriately 
to the discriminanda, he was moved to a distance immediately prior to the point at 
which the correct SD, S-delta behavior was no longer observed. On condition that 
the subject manifested appropriate lever pressing at the closer distance, he was 
returned to the distance where the appropriate discrimination behavior "broke dovm." 
If; once again the subject failed to discriminate the stimulus letters, he was 
placed at the closer distance where the correct responding behavior was observed. If 
the subject again responded according to the defined contingencies, the examination 
was terminated for that subject and a distance visual acuity ratio was formulated. 
A minimum of tx^o successive and consistent threshold crossings were required before 
experimentation V7as terminated for a subject. If a subject failed to generalize 
from the criterion cards to the 20/200 cards, additional fading cards were constructed 
to successively approximate the size of the latter card. 

When a subject ceased responding at a certain distance, and the experimenter 
could not reestablish appropriate discrimination behavior at a distance vrhere the 
subject had been observed to respond appropriately, experimentation was postponed 
until either later in the same day or the following day. This condition occurred 



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several times in conjunction vrith an alteration of the feeding schedule of a subject 

initiated by one of the institution's attendants. 

Results 



The data obtained demonstrate that a subjective measure of distance visual 
acuity is procurable from non-verbal retarded children. Table 1 presents the amount 
of time in hours required to complete the four phases of the experimental study. 

The observed disparity in time required to complete the examination between S-1 
and the remaining subjects was mainly a function of the experimenter's inability to 
identify a suitable reinforcing stimulus which maintained the subject's lever press- 
ing behavior. 

Results are not reported for the tvro adult subjects. 



TABLE 1 
Time in Hours Required to Complete the Four Phases of the Study 
and the Obtained Subjective Distance Visual Acuity Ratios 



Subjects 



Time in Hours 



Phase 



II 



III 



IV 



Total 



Visual Acuity Ratios 
Uncorrected Lens Corrected 



S-1 
S"4 
S-5 
S-6 
S-7 



5.5 

.6 
1.8 
1.2 
2.2 



19.5 
1,0 
2.2 
3.8 
1.8 



42,0 
3.2 
4.0 
5.2 
3,2 



39.0 
2,0 
2.2 
2,8 
3.2 



106.0 

6.8 

10.2 

13.0 

10.4 



20/400 

20/20 

20/23 

20/22 

20/32 



20/130 



20/32 



Subjective measurement of distance visual acuity— phase four. It will be 
recalled that when satisfactory discrimination to the forx^ard and reversed "E'' had 
been achieved in a subject; the measurement of distance visual acuity was undertaken. 

Subject"l. Subject-1 failed to make the required generalization from the 
20/200 to the 20/100-E cards. To determine if the subject's visual acuity threshold 



For a detailed account of the results see Macht (1959) 

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was between the two cards, three nei<t fading carasj e.g., F~A, -5, -6, were constructed 
each being successively reduced to approximate the 20/100 card. The subject success- 
fully discriminated the F-A and F-5 "E" cards, but failed to generalize from the 
F-5 to the F-6 cards. The size differential between the F-5 and F-6 cards was 0.25 
inch on the top and 0.25 inch on the bottom. Figure 1 presents the response data 
for the F-5 and F-6 cards vrhen the subject wore her glasses at 29 inches from the 
discriminanda. Subject-1 made the appropriate discrimination for the F~5 card, but 
failed to do so for the F-6 card. After observing that S™l's lever pressing behavior 
"'broke down" on the F-6 fading card, final acuity measuram-ent was obtained employing 
the F-5 card. Since S-1 had been prescribed 'corrective'' lenses, two measurements 
were taken. Figure 2 presents the response data for the F-S card with glasses on 
and Figure 3 presents the response data for the same card when S-1 did not v/ear her 
glasses. The subject with glasses, discriminated the F-5 card at 95 inches from the 
discriminanda while failing to do so when placed at 119 inches from the stimulus cards, 
I-ilhen the glasses were removed, S-1 appropriately discriminated the F-5 card at 47 
inches from the discriminanda but not at 71 inches from the "E" cards. 

Table 2 summarizes the acuity measurements employing the criterion cards, 20/200, 
and F-5 "E" cards. The subject's measured distance acuity was 20/180 with glasses, 
and 20/AOO without glasses. The data can be understood by viewing the distance the 
subject was placed from the discriminanda and seeing the degree of success in emitting 
the appropriate response. If the subject had successfully discriminated the 20/100 
card at 240 inches then the minimal distance acuity would have been 20/100. However, 
S-1 failed to discriminate beyond the F-5 "E" card (C\75 inch larger than the 20/100 
'E'") and discriminated the F-5 card at only 95 inches with the glasses. Thus the 
distance acuity threshold V7as betvjeen 20/200 and 20/100. Since the discrimination 
broke doi-m" short of half-way between zero and 240 inches from the discriminanda for 
the F-5 card (half the size difference betvjeen the 20/200-20/100 cards) the acuity 
ratio vjas slightly higher than 20/150, i.e., 20/180, while wearing glasses. 



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0-0-0 SD 
x-x-x S- delta 




F-5 F-5 F-6 F- 



F-5 



r - b t -D 



STIMULUS CARDS 



SD 


35 29 18 31 25 23 46 21 


44 


23 


S^ 


39 27 18 31 22 25 41 22 

NUMBER OF CARD PRESF-NTATIGNS 


49 


22 



Fig. 1. R-^spoiisG frequency to F-5 and F-5 cards at 
29 inches in secuence for S-1 v;ith cr].as5cs. 



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en 

DJ 
CO 

o 
a, 

CO 

w 



18 
15 
14 
12 
10 



0-0-0 SD 
x-x-x S-dolta 




-^fcrrr^^ 



29 47 71 95 119 119 95 95 119 95 119 95 
INCHES FROM DISCPJMINANDA 



SD 


22 


14 16 21 19 17 15 24 21 20 


19 


19 




S-A 


21 


17 18 23 22 20 14 22 25 23 

NUf'IBExR OF CARD PRESENTATIONS 


19 


21 





Fig. 2. Subject-1's intra -subject tlireshold crossing 
for the F-5 card v;ith glasses. 



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^ 



to 

CO 

o 

CO 




c-o-o SD 
x-x-x S-dolta 



29 47 29 47 71 47 71 

INC HES FROM DISCRIMINANPA 

SD 25 15 24 13 17 21 ' 18 
S^ 24 19 24 18 18 23 19 

NUMBER OF CARD PRESENTATIONS 



for 



Fig. 3. Subjcct-1's intra-subject threshold crossing 
the F-5 card without glasses. 



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TABLE 2 
Maximum Distances at I'Jhich Subject-1 Discriminated 
the Criterion, 20/200, and F 5 Cards 
with and without Eyeglasses 



Cards 



Distance from Discriminanda 



With Glasses 



Without Glasses 



Criterion 

20/200 

F-5 



240^' 

240" 

95" 



191" 
71" 
47" 



Distance Acuity Ratio 



20/180 



20/400 



Subject°4. Subjective distance acuity measurements obtained from this subject 
revealed that S-4 had a minimal visual acuity ratio of 20/20. Table 3 presents the 
response data for the 20/20 ''E" cards. This subject's lever responding continued to 
be under the control of the "E^' directionality of the 20/20 cards at 240 inches. A 
total of two experimental hours distributed over six sessions was required to complete 
the measurement of the subjective distance visual acuity (phase four) for S-4. 



TABLE 3 
Measurement by the 20/20 Card of Distance Visual Acuity for S-4 



bi stp.r.c^ 


frcn 
land a - 






c 


' — — 














Sd 




Oi.scrini. 


Pres 


3ntf:tioiis 


:.as' 


pons-..s 


Proporti 


ons 


Vi 


:es2 


utat: 


-ons 


responses 


•Proportion 


29 






10 




IC 


1 . 00 








11 







,00 


71^' 






11 




11 


1.00 








11 







.00 


119" 






11 




11 


loOO 








12 







.00 


143^^ 






12 




12 


1.00 








10 







.00 


167" 






12 




12 


1.00 








12 







.00 


191' 






12 




11 


.92 








12 







,00 


215" 






14 




10 


.71 








12 




1 


.08 


240^^ 






16 




13 


.81 








11 







,00 



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Subject-5. This subject's distance visual acuity ratio was 20/23. Table 4 ; 
presents the response data for the 20/20 "E" cards, showing that S-5's lever respond- 
ing "broke down" at 167 inches. Figure 4 graphically displays S-5's intra-subject 
threshold crossing for the 20/20 "E" cards. Evidence is offered that S-5's visual 
acuity threshold was between 143 and 167 inches. Subject~5 required 2.2 hours of 
experimental treatment distributed over six experimental sessions to complete measure- 
ment of the subjective distance visual acuity. 

TABLE 4 
Measurement by the 20/20 Card of Distance Visual Acuity for S-5 



D istance from 


Presentations 


SD 
Responses 


Proportions 








Sd 




Oiscriminanda 


Presentations 


Responses 


Proportio 


29" 




11 


11 




1.00 




12 







.00 


47" 




11 


11 




1.00 




11 







.00 


71" 




10 


10 




1.00 




12 







.00 


95" 




14 


13 




.93 




13 







.00 


119" 




19 


18 




.94 




17 




2 


,11 


143" 




65 


54 




.83 




61 




1 


.01 


167" 




62 


6 




.09 




63 




13 


.20 


Subject-6. 


Subject- 


■6's subjec 


tive 


distance 


visual 


acu 


ity was approximately 



20/22, The response data obtained from the 20/20 "E" cards show that S-6's lever 
responding was controlled by the directionality of the "Es" until he was placed 
215 inches from the discriminanda . The data are presented in Table 5. Figure 5 
shows S-6's intra-subject threshold crossing for the 20/20 "E" cards and demonstrated 
that the subject's threshold was between 191 and 215 inches. The proportion of SD 
responses decreased when the subject was moved from the 191-inch to the 215-inch 
distance. Nine experimental sessions, lasting a total of 2.8 hours, were spent 
completing phase four for S-6. 



=16- 



',r 



to 

CO 

g 

CO 



0~C-G oD 

x-x-x 3"dcll,a 




for 



29 47 71 95 .1.19 143 167 145 143 167 143 167 

INCHBS FROMJDISCRIMINANDA „ „ __ 

SD 11 ■ 11 j.O '' i4""l9 " 19'"'"20 "TS '18'" 20 "'13 "'22 ' 

S^^ 12 11 12 13 17 13 19 17 13 21 13 23 

iM?l£l5L_OL.,i±5M._,fl£l§^ -^ _..__... 

Fig. A. Subject-S's intra-subject threshold crossing 
the 20/ 2Q card. 



-17- 



CO 

w 

CO 

o 

Q-, 
W 
DQ 



14 



12 



10 



o-o-o SD 
x-x-x S-dcilta 




29 47 71 119 143 167 191 215 191 215 191 

INCHES FROM DISCRIMINANDA 



SD 


13 


15 14 13 14 14- 19 25 17 29 


20 




S^ 


13 


13 15 13 12 13 19 26 17 29 

NUMBER OF CARD PRESENTATIONS 


19 





Fig. 5. Subjecl--5's intra-subjGct threshold crossing 
for the 20/20 card. 



-18- 



TABLE 5 
Measurement by the 20/20 Card of Distance Visual Acuity for S-6 



SD 



Sd 



f) instance from 

Di;i >scriminanda Presentations Responses Proportions Presentations Responses Proportior: 



29" 
47" 
71" 
119^' 
143" 
167" 
191" 
215" 



13 
15 
14 
13 
14 
14 
56 
54 



13 


1.00 


15 


1.00 


14 


1.00 


12 


.92 


12 


.85 


10 


.71 


42 


.75 


5 


,09 



13 
13 
15 
13 
12 
13 
55 
55 






.00 





,00 





.00 





,00 





.00 





,00 


3 


.05 


7 


,13 



Subject-7. Several different acuity measurements were taken with S-7 . This 
subject had been prescribed lenses without the benefit of a subjective axaiainationc 
A- detailed account of the procedures and results are to be described in a further 
papar. Table 6 presents tL^ response data for the 2C/30 'F'' cards for S~7 . 
Sub3ect--7's levar responding becama undif ferentiatec. s/c 215 inches from the discrim- 
inanda. Figura 5 graphically shov7s S-7's intra suLj^ct threshold crossing for the 
2"/3j E'" cards. Figure 6 o'rfors evidence that. .3-7 '>• ihrsshold tras between 191 and- 
215 Inches, Based on ther-^i data,, S~7's uncorrecte-l subjec^.ive distance acuity T/as 
23/32, The corrected acvJ-'zy ratio raporfii in Tabli 1 referrad to the observed •-,-, 
perfcrrr.ance with new lensac :;'rescribed 'y ar.. ophtbalrolcgict aftsr S-7 had teen, 
tested by the present procedure. 



-19- 



20 
18 
15 
14 
en 12 
g 10 

CO 

pi; 



.O C-" 



o-o-o 
x-x x 



o- delta 



-X -X— -— X- 






29 47 71 95 119 143 1G7 191 215 




iii^^^l'^'S F,i-U2M_DISCRIHINAN]')A 

SD 18 19 " 17" 18 ""21 20" "T9 "2i '^q'— 05- 

S^ 17 21 16 17 22 21 18 22 20 24 

NUMJ5HR OF CARD PRBSHMTATiONS 



20" 22 22 
20 22 23 



Fig. 6. Subject-7'55 inUra-GubJGcL thrcjihold cro;:^y.ing 
for the 20/30 card v;ithoul: glasf.es. 



-20- 






I 



'i 



TABLE 6 
Measurement by the 20/30 Card for S-7 Without Eyeglasses 













"*' ' ■ ' 




*" 


stance 


from 
landa 


Presentations 


SD 
Responses 


Proportions 




Sd 




.scrimir 


Presentations 


Responses 


Proportion 


29" 




18 


16 


,88 


17 





.CO 


47^' 




19 


17 


.89 


21 





.00 


71" 




17 


17 


1.00 


16 





.00 


95" 




18 


17 


.94 


17 





.00 


119" 




21 


18 


.86 


22 





.00 


143" 




20 


18 


.90 


21 





oOO 


167" 




19 


17 


.89 


18 





„00 


191" 




65 


54 


.83 


65 





.GO 


215" 




67 


11 


.16 


66 


13 


.Iv 


Discussion 















It is apparent from the present research that there are critical features which 
must be incorporated into procedures designed to obtain information from children. 
First, a child's behavior repertoire must be sufficiently inclusive to afford 
ejaission of the response. If a child fails to emit a response an examiner must be 
cautious about infering an absence of ability due to the absence of appropriate 
behavior. The only way to determine if a child "knox-js" somethings or discriminates 
various stimuli, is to obtain an observable behavioral report from him. Without the 
observable report, an examiner is relegated to inferential behavior and, as Meyerson 
and Michael (1960) point out, the inferred conclusions may not be substantiated by 
later empirical investigations. Second, the employed stimulus conditions tnat even- 
tually control responding must be adequately programmed so as not to p.reclude appro- 
priate responding. By employing successive approximations to criterion behavior, 
the experimenter has a povrerful tool which not only maximizes information feedback 
but increases the pre Lability that a child's behavior x^d.11 be reinforceable. 



11- 



la general, the bindings -rom cue preseal :.tudy make suspect Adier's statement 
(1962) that a subjective method of refraction is of little value in children less 
than seven tu eight years of age. The five childreri eaoioyed in the experimental 
sample were seven years of age and younger. Additionally j it is now possible to take 
a somewhat modified view of Adler's earlier statement (1950) that ^'failure to 
accurately measure most children is due to their lack of cooperation and their low 
level of intellectual functioning.'' The more recent interpretation gives attention 
to procedural inadequacies rather than to the presence or absence of soma qu-glity 
attributed to the child. 

By viewing the experimenters i.e., educator or therapist, as the object of 
probable deficiency rather than explaining away unpredicted or unaccountable out- 
comes due to subject inadequacy, one builds "self-correction" into his methods. 



™79... 



i ■ 



lb 



References 

Adler, F. H. Physiology of the eye. St. Louis; C. V, Mosby, 1950. 

Adler, F. H. Textbook of ophthalmology.. Philadelphia ana London: W. B. Saunders ^ 
1962. 

Adler, H. E. & Dalland, J. I. Spectral thresholds in the starling. Journal of 
Comparative and Physiological Psychology , 1959, 52, 438-445. 

Allen, H. F. Testing visual acuity in preschool children. Pediatrics , 1957 > 19, 
1093-1100. 

Blackhurst, R. T. & Radke, E. Vision screening procedures used with mentally retarded 
children — a second report. Sight Saving Review , 1968, 38, 84-88. 

Blough, D. S. Spectral sensitivity in the pigeon. Journal of the Optical Society of 
of America . 1957, 47, 827-833. 

Blough, D. S. A method for obtaining psychophysical thresholds from the pigeon. 
Journal of the Experimental Analysis of Behavior , 1958, 1^, 31-43. 

Blough, D. S. & Schrier, A. li. Sco topic spectral sensitivity in the rhesus monkey. 
Science, 1963, 139, 493-494. 

Duke-Elder, S. The practice of refraction. St. Louis: C. V. Mosby, 1965. 

Elliot, D. N., Frazier, L., & Riach, W. A tracking procedure for determining the 

cat's frequency discriminatioa. Journal of the Experimental Analysis of Behavior 
1962, 5, 323-328. 

English, H. B., & English, A, C. A comprehensive dictionary of psychological and 
psychoanalytical terms. New York: David McKay Company, 1958 « 

Gorman, J. J., Cogan, D. C, & Gellis, S. S. An apparatus for grading visual activity 
of infants on the basis of opticokinetic nystagmus. Pediatrics , 1957, 19^, 1088- 
1092. 



Gtindersen, T. Amblyopia ex anopsia; A preventable form of blindness. Pediatric 
Clinics of North America o 1955, 2, 625. 

Havener, W. H. Synopsis of ophthalmology » St. Louis: C. V. Mosby, 1963, 13-15. 

Heise, G. A. Auditory thresholds in the pigeon. American Journal of Psychology , 
1953, 66, 1-19. 

Kelly, C. R. Visual screening and child development; the North Carolina study . 
Raleigh: North Carolina State College, 1957. 

Lever ett, H. M. Vision test performance of school children, American Journal of 
Ophthalmology . 1957, 44, 508-519. 

Macht, J. E. An operant procedure for measurement of subjective visual acuity in 
non-verbal children. Unpublished dissertation , Arizona State University, 1969 

Meyerson, L. & Michael, J, L. The measurement of sensory thresholds in exceptional 
children: An experimental approach to some problems of differential diagnosis 
and education with special reference to hearing. Monographs in Somatopsycho- 
logy , 1960, 4^. 

-23- 



iry. 



•" J 



• f>'. 



! )• /. 



I 



Sldman, M. Tactics of scientific research. Evaluating experimental data in 
psychology . New York; Basic Books, 1960. 

Sjjigren, H. New series of test cards for deteinnining visual acuity in children. 
Acta Ophthalmologica , 1939, !]_, 67. 

Wolfe, W. G. & Macpherson, J. R. Comparative investigation of methods of testing 



auditory and visual acuity of trainable mentally retarded children. 
Office of Education, Cooperative Research Bureau , SAE 6447, 1960. 



U. S. 



Yarczower, M. , Wolbarsht, M. L., Galloway, W. D., Fligsten, K. E., & Malcolm, R. 
Visual acuity in a stumptail macaque. Science , 1966, 152 , 1392. 



-24- 



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